Various dehydrogenation processes have been proposed to dehydrogenate dehydrogenatable hydrocarbons such as cyclohexanone and cyclohexane. For example, these dehydrogenation processes have been used to convert at least a portion of cyclohexanone into phenol.
Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. However, the world demand for phenol is growing more rapidly than that for acetone.
Other known routes for the production of phenol involve the direct oxidation of benzene, the oxidation of toluene, and the oxidation of s-butylbenzene wherein methyl ethyl ketone is co-produced with phenol in lieu of acetone produced in the Hock process.
Additionally, phenol can be produced by the oxidation of cyclohexylbenzene to cyclohexylbenzene hydroperoxide wherein cyclohexanone is co-produced with phenol in lieu of acetone produced in the Hock process. A producer using this process may desire to dehydrogenate at least a portion of the cyclohexanone produced into the additional phenol depending on market conditions.
For example, U.S. Pat. No. 3,534,110 discloses a process for the catalytic dehydrogenation of cyclohexanone and/or cyclohexanol to phenol over a catalyst comprising platinum and preferably iridium on a silica support. The catalyst also contains 0.5 to 3 wt % of an alkali or alkaline earth metal compound, which, according to column 3, lines 43 to 49, should be incorporated after addition of the platinum since otherwise the resulting catalyst composition has inferior activity, selectivity and life.
In addition, U.S. Pat. No. 4,933,507 discloses that phenol can be produced by dehydrogenating cyclohexenone through a vapor-phase reaction in the presence of hydrogen using a solid-phase catalyst having platinum and alkali metal carried on a support, such as silica, silica-alumina or alumina. The catalyst is prepared by first treating the support with an aqueous solution of platinic acid, etc., to have platinum chloride carried on the support, then treating the support to have an alkali metal compound such as K2CO3 supported thereon, and finally reducing the treated support. The content of alkali metal in the catalyst is preferably in the range of 0.5-2.0 weight % (wt %) in terms of Na2O based on the weight of the support and in the range of 0.2-3.0 wt % in terms of K2CO3 based on the weight of the platinum.
U.S. Pat. No. 7,285,685 discloses a process for the dehydrogenation of a saturated carbonyl compound, such as cyclohexanone, in the gas phase over a heterogeneous dehydrogenation catalyst comprising platinum and/or palladium and tin on an oxidic support, such as zirconium dioxide and/or silicon dioxide. In addition, the dehydrogenation catalyst can further comprise one or more elements of Groups 1 and/or 2, preferably potassium and/or cesium, which are added to the catalyst as aqueous solutions of compounds which can be converted into the corresponding oxides by calcination. In the only catalyst preparation example, an aqueous solution containing CsNO3 and KNO3 is added to a silica/titania support after the support has been impregnated with a solution of SnCl2.2H2O and H2PtCl6.6H2O in ethanol, then dried at 100° C. for 15 hours and calcined at 560° C. for 3 hours.
One problem that has been encountered in the use of supported noble metal catalysts in the dehydrogenation of cyclohexanone is that the activity of the noble metal decreases fairly rapidly unless the metal is well dispersed on the support. However, a typical catalyst produced by directly impregnating a noble metal onto a support tends to result in poor metal dispersion because of non-uniform metal particle sizes. Thus, the resultant catalyst generally deactivates rapidly and so requires frequent reactivation or replacement. Given the high cost of noble metals and the loss in production time involved with frequent reactivation, there is, therefore, a need for a cyclohexanone dehydrogenation catalyst having improved resistance to deactivation.
According to the present invention, it has now been found that an oxide-supported, metal-containing cyclohexanone dehydrogenation catalyst having improved stability and activity, as measured by its unique oxygen chemisorptions properties, can be obtained if, prior to addition of the dehydrogenation metal, the oxide support is treated with a Group 1 or Group 2 metal promoter (i.e., alkali metal or alkaline earth metals) and then calcined under controlled conditions.